Study On The Reasonable Thickness Of Crown Pillar And Slope Stability For Open Pit To Underground Mining In Gushan Mine

Open pit to underground mining is an important method for mining enterprises to develop deeper resources.Backfilling abandoned open pit with tailings not only provides discharge space for tailings treatment of underground mining,but also provides conditions for land reclamation and vegetation restoration within the scope of the pit,which has great application value for the sustainable development of mining enterprises.Based on the engineering background of Gushan Iron Mine,this paper studies the safe thickness of the crown pillar and the stability of the pit slope through theoretical analysis and numerical calculation.Through the study of this paper,we have a better understanding of the disturbance effect of surrounding rock in the condition of pit tailing backfilling,which is of great significance and value for the wider and safe application of the production mode.The conclusions are as follows:?1?Based on the long-term stability of the overlying rock mass in goaf and the safety of the single access roof in the mining process,the stress state of the crown pillar in the open transfer mining is analyzed,the elastic foundation beam model and the cantilever beam model of the shaving load of the crown pillar are established,and the theoretical values of the critical safe thickness of the crown pillar under the conditions of different filling parameters and access span are calculated.?2?Based on Surfer and ANSYS transition platform method,a complex three-dimensional geological model of Gushan Iron Mine is established,and FLAC^3Dsoftware is imported to carry out the numerical calculation of opencast mining under the condition of tailing backfilling.The influence of mining access span and goaf filling parameters on the critical safe thickness of crown pillar is analyzed.Based on the comprehensive judgment of the plastic zone,stress field and displacement field of surrounding rock,the numerical simulation results of the critical safe thickness of the crown pillar under the conditions of different access width and different elastic modulus of the filling body in the goaf are obtained.Based on the results of theoretical calculation and numerical simulation,the critical safe thickness of open transfer mining in Gushan Iron Mine is obtained.?3?According to the capacity of the open pit converted into tailings pond and the mining life of each middle section of the underground ore body,the open pit to underground mining in Gushan Iron Mine is divided into several stages.Through the numerical simulation of each stage,the influence of open pit to underground mining on the dynamic disturbance of the surrounding rock of the pit slope and the backfilling effect of tailings are obtained.?4?According to the displacement characteristics of slope rock mass,it is concluded that the movement of slope rock mass caused by open pit to underground mining is a composite movement mode,which has the common characteristics of sliding and settlement.It is the vector sum of the superposition of the sliding displacement W_L along the slope,the displacement W_D pointing to the underground goaf and the slope displacement W_S caused by tailings backfilling.According to the difference of rock mass movement characteristics in different spatial positions,it is concluded that the slope of the open pit of the open pit to underground mining presents a composite potential failure mode of sliding collapse.Through the analysis and calculation of strength reduction method,it is concluded that the slope of open pit in Gushan Iron Mine can keep stable basically,and the tailings can be used to backfill the abandoned pit,which is beneficial to the slope stability of underground mining.In this paper,there are 57 figures,18 tables,and 108 references.